This invention relates to means and a method for making a constant cross sectional area, pultruded filament-reinforced article, the shape of which varies along its length. More particularly, the invention relates to a novel shaping for use in a pultrusion process where the die has a substantially rectangular shape of constant cross-sectional area but wherein the height and width of the shape are infinitely adjustable.
The term "continuous pultrusion" as used herein involves drawing a bundle of filaments from a source thereof; wetting the filaments with a desired thermosettable polymer resin; pulling the resin-wetted bundle through a shaping die to align the fiber bundles and to manipulate it to the proper cross sectional configuration for laying it down in a mold; and curing the resin in the mold while maintaining tension on the filaments. The most common filament reinforcements are rovings of glass fibers. The most commonly used resins are based on epoxy polymers. Since the glass rovings progress completely through the pultrusion process without being cut or chopped, the resultant products have exceptionally high longtitudinal strength. They are, therefore, uniquely suited for applications such as fiberglass leaf springs.
Pultruded articles generally have a constant cross sectional area. This is because the filament reinforcement occupies a fixed cross sectional area when impregnated with a suitable amount of thermosetting resin. It is important in achieving parts with uniform physical properties to evenly distribute the fiber filaments throughout the completed part. Where a part such as a non-constant cross section, bow shaped, semielliptical spring is desired, some provision must be made to distribute the fiberglass reinforcements evenly to achieve consistent high quality.
U.S. Pat. No. 3,530,212 to Kienle et al, assigned to the assignee hereof, relates to a method of making glass resin laminates of constant cross sectional area and varying shape. In the preferred practice of that invention, resin impregnated rovings are drawn through an open ended die having uniform cross section, the width of which is preferably equal to or slightly less than the width of the article to be molded and the height of which is equal to or slightly greater than the thickness of the article. By being drawn through the die, the rovings are brought together in side-by-side relationship. In order to distribute the fibers throughout the article, the tension on the rovings is released as the compression mold is closed to allow the rovings to fan out and fill the cavity. The mold is then heated to cure the resin and complete the part. It would be preferable in pultrusion processes of the type described in Kienle et al to maintain tension on the rovings as they progress through the pultrusion apparatus without sacrificing uniform filament distribution in molded articles. It would also be desirable to align the filament bundles in substantially parallel, side-by-side relation, before they are laid into the compression mold.
Accordingly, it is an object of the invention to provide a method of molding an article by the pultrusion process where the article has a constant cross sectional area but varies in width and thickness along its length.
Another object of the invention is to provide a novel shaping die which is capable of laying down fiber bundles in compression molds to produce foursided pultruded articles of constant rectangular cross sectional area which may vary infinitely in width and thickness.
A more particular object of the invention is to provide a method of making a bow-shaped, filament reinforced, resinous composite leaf spring having a constant cross sectional area by a pultrusion process. Another specific object is to employ a specially adapted shaping die to assist in the manufacture of articles such as arcuate, bow-shaped, composite leaf springs.